1. Field of the Invention
This invention pertains in general to transmission of uncompressed video and audio data over a serial link, and in particular to transmission of uncompressed video and audio data over a single serial communication channel at a fixed data rate.
2. Background of the Invention
It is well-known in the art to represent uncompressed video data by pixels, lines, and frames. Each video format is characterized by a number of pixels per line, number of lines per video frame, and number of frames per second. These characteristics determine the pixel clock rate at which pixels are generated, the line rate at which a line of pixels is generated per second, and the frame rate at which video frames are generated.
For example, 720×480 p @60 HZ video format has the following characteristics:
Pixels per line=720
Lines per frame=480
PIXEL_CLK rate=27.027 Mhz
Line rate=31.5 KHz
Frame Rate=60 Hz
XGA 1024×768@60 Hz video format has the following characteristics:
Pixels per line=1024
Lines per frame=768
PIXEL_CLK rate=65.0M Mhz
Line Rate=48.36 KHz
Frame Rate=60 Hz
When the data selected from a group of various video formats is transmitted from a video source, such as a DVD, to a video monitor over a serial link in real time, the receiving side should be able to recover the original data for all video formats. In order to properly reconstruct original data at the destination side, the data needs to be carried over the communication channel along with video synchronization signals HSYNC and VSYNC and the timing signal PIXEL_CLK.
The newly adopted DVI (Digital Visual Interface) and HDMI (High Definition Multi-Media Interface) standards use four pairs of links to transmit video and audio data such that three pairs of links are used for transmission of video data and one pair is used for transmission of the timing signal. Both DVI and HDMI, as well as other newly proposed schemes, are capable of supporting various video formats. However, by requiring an extra communication channel to transmit the timing signal these standards significantly increase the cost of data transmission.
Many applications currently require that uncompressed audio and video signals be transmitted over a serial link having a single communication channel. To this end, all video and audio data as well as a timing signal have to be transmitted over the single channel. Existing single-channel communication systems that do not have a separate channel for the timing signal transmit data at a fixed data rate of the communication channel. Because pixel clock rate varies for each video format, existing single-channel communication systems do not support transmission of video data selected from a group of various video formats over the single communication channel of the fixed data rate.
Moreover, transmitting video data over a single communication channel requires a great bandwidth so that a large amount of information can be sent at a given amount of time. Video data has an active period and blanking period. The blank period constitutes about 20% of the total communication bandwidth and does not carry useful display information. Accordingly, blanking period required by certain display devices makes a part of the available bandwidth not usable. Many existing schemes utilize the blanking period to carry control information or audio data. However, the bandwidth requirement of control information and audio data is very minimal. Accordingly, the current solutions still do not address the bandwidth problem in communication systems that transmit video data.
It is therefore desirable to provide a framing format that has the flexibility of supporting transmission of data selected from a group of various video formats and pixel clock rates over a single communication channel. In addition, it is desirable to provide a mechanism that saves communication bandwidth by transmitting only the active video data selected from a group of various video formats over a single communication channel.